An X-ray tube of this kind is known from U.S. Pat. No. 3524379. It is drawback of a tube described therein that the distance between the anode and the exit window must be comparatively long or that the tube has a comparatively low efficiency due to a limited X-ray yield of an electron beam to be directed onto the anode, which is due to the focus geometry and shadowing.
EP 275592 discloses an X-ray tube which mitigates the above drawbacks by utilizing an exit window which also acts as an anode. Even though a minimum distance is thus realized between the anode target face and the exit window, the operation of such a tube is not satisfactory in cases where a comparatively intensive X-ray beam is required. This is not so much due to the low efficiency between electron beam and radiation yield, but rather to a limited electron loadability of a sufficiently thin exit window.